This application claims the priority of Korean Patent Application No. 10-2003-0048314 filed on Jul. 15, 2003 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of Invention
The present invention relates to multimedia data transmission through a network, and more particularly, to a network device and data transmission method for efficiently transmitting multimedia data between nodes in a mobile ad hoc network (hereinafter, referred to as ‘MANET’) environment.
2. Description of the Related Art
Generally, since multimedia data such as audio and video data (hereinafter, referred to as ‘AV data’) require a lot of bandwidth, efficient data transmission between a data-sending party and a data-receiving party through a network may be achieved by means of a method of measuring currently available bandwidth and then changing an AV data transmission mode according to the measured bandwidth. A more detailed description of such a method will be made with reference to FIGS. 1 and 2.
FIG. 1 is an exemplary view schematically illustrating a conventional video transmission system in a network. The system comprises a video compression/file generation unit 100, a video server 110, and at least one video client 130. The video compression/file generation unit 100 receives raw video data and constructs the received data in multiple levels that in turn are encoded according to different data compression rates and then stored as files, respectively. In a case where the video client 130 requests video data transmission, the video server 110 measures the bandwidth available in a network 120 and selects a level corresponding to the measured bandwidth from the video compression/file generation unit 100. Then, the video server sends video data compressed with the selected level to the video client 130.
FIG. 2 is an exemplary view specifically illustrating the configuration of the video server 110 shown in FIG. 1. The video server 110 comprises a receiving unit 112 for receiving the compressed video data from the video compression/file generation unit 100; a transmission unit 114 for sending data received from the receiving unit 112 to the network 120 and measuring bandwidth of the network 120; and a control unit 116 for selecting the level according to the measured bandwidth. The transmission unit 114 periodically measures bandwidth even during data transmission. The bandwidth measurement is made based on end-to-end measurement, i.e. server-to-client measurement and uses a data transmission rate or data receiving rate. The data transmission rate denotes the number of bytes sent for a given response time period, whereas the data receiving rate denotes the number of bytes received for a given response time period. If there is a change in bandwidth during the periodic measurement of the bandwidth by the transmission unit 114, the control unit 116 selects a level corresponding to the measured bandwidth for the receiving unit 112, and the receiving unit 112 extracts a compressed video file corresponding to the selected level from the video compression/file generation unit 100 and then sends the extracted file to the transmission unit 114.
The data transmission method illustrated in FIGS. 1 and 2 may be efficient in a case where data transmission channels are fixed in the same manner as a wired network or where the positions of network devices using the data transmission channels are stationary. However, it may be difficult to apply the above method to cases where the status of a transmission channel or network is greatly changed as in a MANET environment. That is, a network terminal constituting a MANET requires a lot of additional resources due to limitations on processor performance, memory, power supply and the like in order to compress raw AV data with various levels and store the compressed AV data. Further, if only the bandwidth of the network is measured to select the compression level for the data transmission, it is difficult for a user to obtain satisfactory AV data in a MANET environment of which the status such as topology, time delay and receiving intensity dynamically varies. Accordingly, there is a need for an efficient AV data transmission method suitable for a MANET environment.